Rework gradle-build system

[TBlueF]

Complete overhaul of the gradle build system to build the project, should be way more sensible and modern :)

Also uses the individual platforms ways of library-management (on paper, fabric, forge and neoforge) to properly load the flow.math library which can't be relocated since it is part of the API.

Fixes: #516

[TBlueF]

Missing: automatic publishing to the various plugin/mod-repos